Variation of the thickness ratio b/R_d as a function of the ratio h_z/R_d, for the thin and thick stellar disks and the H I and H₂ disks subcomponents. Filled circles represent the optimal solutions found after the application of the cross-entropy algorithm, as described in Sect. 2.2.2 of the main text. Solid lines represent 4th-order polynomial fits to the distribution of points associated with each calculated relation.